Everett police said that a woman called 911 at about 9:30 a.m. Tuesday to report what she believed were credible threats made by her grandson to shoot students at ACES High School, where he is a student.

Officers met with the grandmother at her Everett home, where she showed officers excerpts from her grandson’s journal. Officers were also told the grandson had a rifle stored in a guitar case.

According to probable cause documents, the journal contained statements and detailed plans to shoot students and use homemade explosive devices at the school.

"I’m preparing myself for the school shooting. I can’t wait. My aim has gotten much more accurate … I can’t wait to walk into that class and blow all those (expletive) away.

“I’ve been thinking a lot … I can make this shooting/bombing at Kamiak infamous. I need to get the biggest fatality number I possibly can. I need to make this count. I’ve been reviewing many mass shootings/bombings (and attempted bombings). I’m learning from past shooters/bombers’ mistakes, so I don’t make the same ones."

Probable cause documents also said the journal “contains a ‘coin flip’ that he did to decide whether his target would be Kamiak High School or ACES High School, then wrote about how ACES won the flip and would be his target.”

His grandmother told officers that her grandson had recently purchased inert grenades, which he discussed making “live” in his journal by filling them with black powder, according to police documents. He also wrote about making pressure cooker bombs and where and in what order he would be placing his explosives, documents said.

Police contacted school officials about the alleged threat, and then arrested the student at ACES High School. Police said he was carrying a knife and marijuana.

He was booked into the Snohomish County Jail on probable cause on suspicion of attempted murder "due to planning and taking substantial steps toward executing a school shooting," as well as assault, investigators said.

Police said once the suspect was at the Everett Police Department South Precinct, he managed to get one of his hands out of the handcuffs and then ran across the parking lot. As he ran, with an officer in pursuit, he fell to the ground and then “mule-kicked” the officer in the thighs and lower torso, police said.

Detectives served a search warrant at the grandmother’s house and seized the journal, a rifle, military-style inert grenades and other evidence, according to investigators.